Manufacture of remanent reed switch

ABSTRACT

A technique for the fabrication of a sealed remanent reed, selflatching magnetic switch is described. Appropriate magnetic properties are developed through a series of processing steps terminating first in a strand anneal of round wire; secondly a stamping operation which results in some mechanical working and, consequently, physical hardening of the magnetic alloy; and, finally, in a terminal phase-precipitation anneal.

United States Patent [19] Archer et al.

[ 1 MANUFACTURE OF REMANENT REED SWITCH Inventors: Wendel Edward Archer,Gahanna,

Ohio; Karl Martin Olsen, Madison, N.J.; Paul William Renaut, Columbus,Ohio Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Filed: Feb. 22, 1972 Appl. No.: 227,762

[73] Assignee:

U.S. Cl. 29/622, 200/166 CM, 335/153 Int. Cl. H0lh 11/00 Field of Search29/622, 630C; 200/166 C,

References Cited UNITED STATES PATENTS 1/1968 Gould 335/153 Apr. 23,1974 3,251,121 5/1966 Prival 29/622 3,369,291 2/1968 Shaffer 29/6223,443,312 5/1969 Morigama 29/622 Primary Examiner-Charles W. LanhamAssistant ExaminerR0bert M. Rogers Attorney, Agent, or FirmG. S. lndig 57] ABSTRACT 12 Claims, 1 Drawing Figure BACKGROUND OF THE INVENTION 1.Field of the Invention Theinvention is concerned with the fabrication ofa particular type of magnetic self-latching switch-generically known asferreed." The particular type of concern utilizes the remanent magneticmaterial responsible for latching as a part of the reed structure whichsupports the contacting regions of the switch (in contrast to the moreusual type in which the remanent member is external to the switch).

2. Description of the Prior Art The Bell System Technical Journal forJanuary 1960 at page 1 et seq. describes a class of switching devicesdesignated as ferreeds. These devices are characterized by sealedmetallic contacts which are included within a magnetic circuit whichalso includes at least one remanent magnetic member. The remanentmember/s which are switched, generally by means of an encircling wirecoil, has sufficient remanent magnetization so that the contacts may beretained in either the opened or closed condition without continuousexpenditure of energy.

At this time ferreed structures are in prevalent use throughout theworld. They are of particular significance in modern telephony and manymillions of these devices are in use in telephone electronic switchingsysterns.

The usual ferreed structure in use at this time involves a pair ofmagnetically soft reed members supporting contacting regions, with thesereed members magnetically coupled to one or more remanent membersgenerally external to the switch itself. Design variations suggested atabout the time of the development of the prototype device include asimplified structure in which the reed members themselves include or areconstructed of a remanent magnetic material (see Bell System TechnicalJournal, supra, and US. Pat. No. 3,059,075).

The inherent advantages of the remanent reed structure are manifold.Elimination of external remanent magnetic members inherently leads tofabrication economy as well as to size reduction. Under manycircumstances, the internal remanent reed structure may be operated withsome saving in power as well.

Despite the apparent advantages inherent in the internal remanentfreedstructure it has not found prevalent commercial use. In general,continued manufacture of the more costly, larger structure using theexternal remanent circuitry is ascribed to certain manufacturingdifficulties associated with the remanent reed device. Theprimarydifficulty involves the actual formation of the reed. This operationdesirably takes the form of a simple stamping (involving flattening of around wire form )Qlt has been found that this operation, as carried outon material of appropriate magnetic properties, frequently results insufficient embrittlement to cause fracture.-

The foregoing assumes use of an alloy composition generally known asRemendur. This material is nominally 50-50 cobalt-iron alloy with smallvanadium addition. Development of the appropriate remanence (of theorder of at least 10,000 gauss) involves one or more hardeningoperations.

SUMMARY OF THE INVENTION A series of critical processing steps-permitsexpedient fabrication of a sealed remanent reed, self-latching magneticswitch structure. Processing terminates in a sequence of a wire strandanneal (sometimes supplemented by slight mechanical working), followedby a stamping operation and, finally, by a phaseprecipitation anneal.Detailed parameters for these three procedures as well as forpreliminary procedural steps are described in the Detailed Description.

The composition utilized for the remanent portion of the reed (and theentirety of one or more reeds may be of such material) is the usualRemendur composition, i.e., 40 to parts by weight cobalt, 25 to 60 partsby weight iron, and l to 5- parts by weight vanadium. Preferredcompositions as well as possible minor additives are specified underSection 2' of the Detailed Description.

The nature of the fabricated Remendur reed, particularly its surfacecharacteristics, have, in the past, given rise to an additional problem,i.e., formation of a durable hermetic seal where the reed emerges fromthe capsule. A preferred embodiment of the invention is directed to thematerials and procedure for overcoming this difficulty.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a front elevational viewof a ferreed structure fabricated in accordance with the invention.

DETAILED DESCRIPTION 1. The FIGURE The FIGURE depicts a prototyperemanent reed structure illustrative of those contemplated forfabrication in accordance with the invention. A detailed description ofthis device as well as a number of variations is contained in theaforementioned US. Pat. No. 3,059,075. The FIGURE depicts a glassenvelope 1 containing two reeds, 2 and 3, each of which is provided withcontacting regions 4 and 5, respectively. The larger part of each ofreeds 2 and 3 is flattened from a round wire of the cross-sectionalconfiguration retained by unflattened projecting portions 6 and 7. Suchportions, 6 and 7, enter the envelope 1 through glass seal regions 8 and9. While a variety of circuit arrangements are possible and variationsare in actual use, the device depicted entails two separate windings, 10and 11, the first of which, when suitably energized by means not shown,results in polarization of reed 2 in either of the two permitteddirections while the second, coil 11, also when suitably energized bymeans not shown, results in polarization of reed 3. This particulararrangement, which, in more sophisticated variations, may involveoverlapping coils, permits separate control of each of the reeds and is,therefore, adaptable to use in a cross-point array.

Operation of the device is simple. Polarization of reeds 2 and 3 in thesame direction (e.g., north-south from left to right) accomplishesclosure while magnetization of reeds 2 and 3 in opposite directions(e.g., north-south for reed 2 and south-north for reed 3, both from leftto right) results in open circuit. As described above, the nature of theremanent material, of which at least a portion of at least one of reeds2 and 3 is constructed, is such that either closed circuit or opencircuit may be maintainedwithout expenditure of energy, i.e., theremanent magnetization is sufficient to overcome the natural restoringforces of the structure and maintain closure.

Variations on the structure involve possible use of permanent bias ofone'reed, for example, by constructing it of a permanent magneticmaterial which is not switched during operation or by use of a separatemagnetic biasing element, incorporation of any number of additionalreeds and/or contacts, and, as indicated, a variety of circuitarrangements.

2. Remanent Reed Composition It has been indicated that the remanentmaterial utilized is a member of the class of materials sometimesreferred to as Remendur. It has been indicated that the full range ofthis compositional class is from 40 to 75 parts by weight cobalt, 25 to60 parts by weight iron, and l to parts by weight vanadium.Compositional variations as well as preferred ranges are set forth inU.S. Pat. No. 3,364,449. As there indicated, the nominal (and preferred)composition contains approximately equal amounts of cobalt and iron witha preferred range for the major ingredients being specified as from 45to 65 parts cobalt, remainder iron. The preferred range of vanadium,included to control coercivity, is from 2 to 4 parts by weight based on100 parts by weight of the three ingredients, cobalt, iron, andvanadium. Additional ingredients may include manganese contained tominimize the deleterious effect of any sulfur inclusion (ordinarily upto about one part by weight on the above basis) and possibly minoramounts of silicon and aluminum (either in amount of less than one partby weight on the above basis). These last two ingredients serve to bindoxygen which may also be deleterious in processing. In addition to theintentional ingredients set forth, there are tolerable amounts ofordinarily encountered impurities. Such impurities, the total amount ofwhich does not exceed one part by weight on the above basis, may includenickel, carbon, copper, and sulfur.

3. Processing A. The Remanent Magnetic Material 7 The compositiondesignated is known as Remendur only when possessed of such intermediatehardness as to result in a remanent magnetization of the order of atleast 10,000 gauss. In a soft magnetic state, the composition issometimes known as Permendur, while in its hardened state, it issometimes known as Vicalloy. Development of the requisite degree ofmagnetic hardness necessarily entails both cold working and phaseprecipitation hardening. The invention is, in large part, based on theparticular manner in which these procedural steps are carried out. Whilethe most significant processing steps from the inventive standpoint arethe terminal three steps (numbered 5 (or 5 plus 5A), 6 and 7), thefollowing description specifies appropriate preliminary steps startingwith the formation of the alloy composition itself.

Step I. A melt is prepared of initial ingredients. Suitable ingredientsareelectrolytic cobalt, electrolytic iron, ferrovanadium (an alloy ofvanadium and iron) and electrolytic manganese. The ingredients aremelted (melt temperature about I550C). Temperature is maintained for aminute or two to ensure thorough mixing and an ingot is formed bycooling.

Step 2. The ingot is hot worked at a temperature between 900C and 1250C.Working may take the form of rolling, swaging, or extrusion. Hot workingis continued to an expedient dimension, e.g., to a diameter of aboutone-fourth inch. This step ordinarily involves many passes.

Step 3. The hot worked body is softened by heating to a temperature ofat least 750C and quenching at a rate sufficient to avoid significantphase precipitation. This is ordinarily accomplished by rapid immersionin ice brine. Room temperature is attained in a period of substantiallyless than 1 minute.

Step 4. The quenched rod is cold worked to the desired final dimension(cold drawing to a round wire diameter of from 50 to 10 mils is common).

Step 5. The first of the special procedures considered responsible forexpedient device fabrication in accordance with the invention involves astrand anneal. in accordance with this step, the wire is softened byheat treatment to result in a tensile strength of a maximum of about200,000 p.s.i. and an elongation of a minimum of about 10 percent. Anillustrative treatment entails maintenance at a temperature over a rangeof from about 850C to l050C. Maintenance at this temperature should befor a minimum of at least about 5 seconds with the upper time limitbeing noncritical and determined on the basis of expedience. Inaccordance with one procedure found satisfactory, the wire is passedthrough a 3 foot hot zone at a rate of about 6 feet per minute therebyresulting in maintenance at a temperature approaching that of the zonefor a period of about fifteen seconds. Immediately following thisheating the wire is passed through a water cooled chamber to chill it ata rate fast enough to prevent phase precipitation and associatedhardening. For a variety of reasons, this step is carried out in areducing atmosphere, e.g., hydrogen or cracked ammonia. While inprinciple inert atmosphere is permissible, from a practical standpoint,it is more expedient to operate with a reducing atmosphere than to usethat degree of care necessary to exclude minor quantities of oxidizingingredients from commercial inert gases. The purpose of the reducingatmosphere or, more generally, of the non-oxidizing atmosphere, is toavoid formation of surface oxide, primarily vanadium dioxide, which, dueto its abrasive qualities, results in rapid die wear during step 6. Useof such a non-oxidizing atmosphere is also desirable to provide arelatively clean surface for subsequent plating for contact formation asper B below.

Step 5a. While from the standpoint of device properties, a strandanneal, as described, is adequate to prepare the material for the coldworking of Step 6, certain practical considerations may dictate avariation. For example, it has been observed that the final reedevidences differing magnetic properties as between the flattened portionwhich carried the contact and the still round portion desirably retainedfor sealing purposes. From the standpoint of manufacturing expedience,it may be desirable to so treat the reed as to make these propertiesmore nearly equal. While this will have no significant effect on deviceoperating characteristics, it may, for example, be expeditious by reasonof such practical considerations as the specification of wire propertiesfor the intermediate product which is about to undergo the processingspecified in Step 6. A possible approach in this connection is to use aslightly hardened wire at this stage. This may result, for example, froma cold working following the strand anneal already specified at Step 5.This cold working, which would be sufficiently slight so as to permitthe wire to be within the maximum allowable tensile strength values,might take the form of an area reduction of as little as 20 percent orpossibly as great as 50 percent. This procedure is to be consideredoptional.

Step 6. This is a stamping operation. During this step, the round wireresulting from Step 5 or Step 5 and Step 5a is flattened to produce theenclosed region of the reed (while retaining the round crosssectionalconfiguration of that portion of the member which is hermetically sealedto the envelope). This stamping operation may also include chopping thereed to desired length. Properties developed during Step 6 or processingadvantages gained during Step 6 involve the flattening action only.Properties developed by the stamping operation include a coercivity ofabout 30 to 60 oersteds and remanent magnetization values of 7,000 to10,000 gauss. Further improvement in properties are obtained by a phaseprecipitation treatment as described in Step 7.

Since the wire produced by the series of procedures terminating withStep 5 or Step 5a ordinarily evidence some curvature, it is usual tostraighten the wire at this time. Ordinarily the wire leaving Step 5 or5a is first straightened, then flattened, and finally chopped into thedesired length, in that order. The effect of straightening on mechanicalor magnetic properties is slight.

An additional minor mechanical treatment which may be carried out atthis time involves barrel tumbling in liquids containing abrasiveparticles and/or other means for removing any burring or other surfaceirregularities produced ,by the mechanical stamping operation.

It has been observed in general that the degree of cold working duringthe stamping operation is of relatively small consequence with regard tothe final developed characteristics. For example, starting with a rounddiameter of 21 mils, flattening to a 5 mil specimen on theone hand and8or 9 rnils on the other resulted in no significant variation in finalmagnetic properties. in general, a thickness reduction of at least about40 percent (representing the fraction of the least final cross-sectionaldimension divided by the unflattened wire diameter) is-sufficient atthis stage to result in properties adequate for device operation.

Step 7. The final processing step involves phase precipitation carriedout at such temperature and for such time'as to develop the desiredvalues of remanent magnetization and coercivity. For devices to whichthe invention is directed, it is generally desired that remanentmagnetization lie within the range of from 10,000 gauss to 20,000 gauss,and that the coercivity lie within the range of from 10 oersteds to 50oersteds. These values are a measure of the properties for both theround flattened portions of the reed. It has been determined that bothmagnetic characteristics result from heat treatment of the reed attemperatures within the range of from 550C to 670C for a period of fromone-half to 6 hours. Extensive experimentation has indicated thatexcessively longer times and/or higher temperatures will result in alowering of both the remanent magnetization and coercivity to valuesbelow the specified level. Shorter time and/or lower temperature resultsin retention of higher values of coercivity but does not causedevelopment of desired remanent magnetization.

It has been indicated that a preferred embodiment involves the manner inwhich the protruding portion of the reed is hermetically sealed to theenvelope. it has been indicated that use of a non-oxidizing or,preferably, a reducing atmosphere in Step 5, in avoiding formation ofsurface oxide, is of benefit in reed stamping and plating operations. Inaddition, it has been found that superior hermetic seals are produced byother processing steps. These steps, inclusion of which with Steps 1through 7 above constitutes this preferred embodiment, are nowdescribed.

Step 2a. Following hot working, the surface oxide layer is removedeither mechanically or chemically. While ordinary pickling with strongacid solution is of benefit, it has been found most desirable to resortto mechanical processing such as grinding or milling. Concern here isprimarily with surface smoothness thereby obtaining surface conditionson the rod which will permit its processing into wire free from surfacedefects. Such wire is essential for hermetic sealing since thewire-to-glass seal appears to be primarily compressive (essentiallynonchemical).

Step 3a. Following quenching, it is observed that a very light oxide hasagain formed, and this too is removed, for example, by grit blasting. Analternative procedure involves pickling. It may be possible to eliminateStep 2a and perform the entire surface removal at this stage. Attemptsto carry out the entire grinding or milling operation at this stage havehowever, resulted in some fracture during the cold working of Step 4. Itis possible that the entire surface removal may be performed on smallerdiameter rods, whether obtained by additional hot rolling as in Step 2or by cold working quenched rods as in Step 4.

Step 3b. Past experience has indicated that Remendur treated inaccordance with Step 3 is amenable to the requisite cold drawing orother cold reduction without use of a metallic plating. Less expensivelubricating techniques using oils or dry lubricants have generally beenconsidered sufficient. In accordance with the preferred embodiment ofthis invention, however, it is found that use of a copper or other softmetal, e.g., silver or tin, coating usually applied electrochemicallyor, alternatively, of other chemical coating materials such as zincphosphate, borax, or inorganic oxalates, not only aids in lubricationaction but also provides a protective layer which facilitatesfabrication of wire with a more perfect surface, desirable for hermeticsealing. Consistent with prior practice, any such coating material maybe removed, generally by chemical etching, prior to final drawingthrough diamond dies (as distinguished from carbide dies). Thisgenerally corresponds with a diameter of the order of mils. Apermissible alternative at this stage is to retain the copper of otherpermissible soft metal plating (organic coating as well as tin or otherlowmelting metals must be removed-the final configuration must becapable of withstanding the hermetic sealing temperature of between 600and l400C).

Still with a view to maintaining a high degree of surface perfection tooptimize hermetic sealing, one or more additional strand annealsstarting at a diameter of about 60 mils is introduced to avoid surfacescoring. Such anneal may take the form of 3 feet per minute passagethrough a 3 foot hot zone to reach temperatures of 850C to l050C for aperiod ofabout one-half minute followed by passage through awater-cooled chamber to reduce rapid cooling.

B. Contact Formation The contacting portions of the reeds are providedwith suitable platings in the usual manner. In general, a simple singlelayer of hard gold (e.g., cobalt-hardened gold produced fromcitrate-buffered cyanide bath) is adequate. Plating thickness, again notunusual, is not critical and may be within the range of from 0.5 tomicrons. Due, however, to the usually small dimensions, particularly thegap dimension of the structure, it is ordinarily desirable to maintainthickness uniformity within 1 50 percent.

C. Hermetic Sealing The other operation which deserves discussion hereinvolves the hermetic seal of the protruding reed portion to theenvelope material. The requirements are common to glass-to-metal sealsin other arts. Appropriate temperature coefficient of expansion toclosely match that of Remendur may be accomplished by use of lead baseglass compositions or other appropriate materials. It has been indicatedthat under general circumstances thebond is considered to be primarilycompressive. Accordingly, the glass envelope material softened byheating flows around the protruding reed. On cooling, compressivestresses are set up in the seal area by deliberate design due to thevery slight mismatch of the coefficient of expansion of the glass andthe reed material. The best hermetic seals have been prepared inaccordance with the preferred embodiment of this invention, i.e., by useof Steps 2a, 3a, and 3b.

The temperature-sensitive nature of the desired device properties of theRemendur reeds imposes a further requirement on the sealing operation.It has been found that maintenance of the reed at temperatures aboveabout 800C even for the brief periods of about 6 seconds resultingduring sealing may result in a reduction of as much as 20 percent incoercivity.

What is claimed is:

1. Process for fabrication of a hermetically sealed remanent reed,self-latching magnetic switch comprising a sealed envelope containing atleast two protruding reed members, each of said members including anelectrically contacting surface, in which at least a portion of at leastone of the said reeds consists essentially of an alloy containing from40 to 75 parts by weight cobalt, 25 to 60 parts by weight iron, and l to5 parts by weight vanadium, in which said body portion is produced by aseries of processing steps including hot working, heat treatment,quenching, cold working, and phase precipitation hardening, so resultingin a remanent magnetization of at least 10,000 gauss and a coercivity ofat least 10 oersteds, characterized in that the said series ofprocessing steps concludes with operations in which a round wire bodyportion of the said alloy is strand annealed so as to give the said bodyportion a heat treatment equivalent to maintenance at a temperature of850C to 1050C for a period of from 10 seconds to 15 minutes and ischilled so as to result in an elongation of at least 10 percent and amaximum tensile strength of 200,000 psi, is flattened to a thicknessreduction of at least 40 percent, said figure being the fraction of theleast thickness dimension after flattening divided by the wire diameterbefore flattening, the said wire prior to flattening having the saidelongation and maximum tensile strength followed by precipitationhardening resulting from annealing in a nonoxidizing atmosphere at atemperature from 550C to 670C for a period of from one-half to 6 hours.

2. Process of claim 1 in which the said values of elongation and tensilestrength result from specified processing including strand anneal inwhich the said round wire is produced by cold working a quenched body.

3. Process of claim 2 in which the said round wire is produced by coldworking a hot worked body which is softened by heating to a temperatureof at least 750C.

4. Process of claim 2 in which said specified processing terminates witha cold working procedure in which the area of the wire is reduced byfrom 20 percent to 50 percent.

5. Process of claim 1 in which said alloy consists essentially of from45 to 65 parts cobalt, iron to total parts cobalt plus iron, and 2 to 4parts vanadium.

6. Process of claim 5 in which the cobalt and iron content of the saidalloy are approximately equal.

7. Process of claim 1 in which a surface layer is mechanically removedfollowing hot working.

8. Process of claim 7 in which a surface layer of said wire ischemically removed subsequent to quenching.

9. Process of claim 8 in which the said wire is coated subsequent tosaid chemical removal of the said surface layer.

10. Process of claim 9 in which the said coating consists essentially ofcopper produced by electroplating.

11. Process of claim 10 in which the copper coating is removed prior tothe termination of cold working.

12. Process of claim 1 in which the envelope consists essentially of alead base glass and in which hermetic sealing to the protruding portionof the said reeds is accomplished by heating at least the encompassingportion of the envelope to a temperature of from 600C to 1400C andcooling to solidify the envelope.

1. Process for fabrication of a hermetically sealed remanent reed,self-latching magnetic switch comprising a sealed envelope containing atleast two protruding reed members, each of said members including anelectrically contacting surface, in which at least a portion of at leastone of the said reeds consists essentially of an alloy containing from40 to 75 parts by weight cobalt, 25 to 60 parts by weight iron, and 1 to5 parts by weight vanadium, in which said body portion is produced by aseries of processing steps including hot working, heat treatment,quenching, cold working, and phase precipitation hardening, so resultingin a remanent magnetization of at least 10,000 gauss and a coercivity ofat least 10 oersteds, characterized in that the said series ofprocessing steps concludes with operations in which a round wire bodyportion of the said alloy is strand annealed so as to give the said bodyportion a heat treatment equivalent to maintenance at a temperature of850*C to 1050*C for a period of from 10 seconds to 15 minutes and ischilled so as to result in an elongation of at least 10 percent and amaximum tensile strength of 200,000 psi, is flattened to a thicknessreduction of at least 40 percent, said figure being the fraction of theleast thickness dimension after flattening divided by the wire diameterbefore flattening, the said wire prior to flattening having the saidelongation and maximum tensile strength followed by precipitationhardening resulting from annealing in a non-oxidizing atmosphere at atemperature from 550*C to 670*C for a period of from one-half to 6hours.
 2. Process of claim 1 in which the said values of elongation andtensile strength result from specified processing including strandanneal in which the said round wire is produced by cold working aquenched body.
 3. Process of claim 2 in which the said round wire isproduced by cold working a hot worked body which is softened by heatingto a temperature of at least 750*C.
 4. Process of claim 2 in which saidspecified processing terminates with a cold working procedure in whichthe area of the wire is reduced by from 20 percent to 50 percent. 5.Process of claim 1 in which said alloy consists essentially of from 45to 65 parts cobalt, iron to total 100 parts cobalt plus iron, and 2 to 4parts vanadium.
 6. Process of claim 5 in which the cobalt and ironcontent of the said alloy are approximately equal.
 7. Process of claim 1in which a surface layer is mechanically removed following hot working.8. Process of claim 7 in which a surface layer of said wire ischemically removed subsequent to quenching.
 9. Process of claim 8 inwhich the said wire is coated subsequent to said chemical removal of thesaid surface layer.
 10. Process of claim 9 in which the said coatingconsists essentially of copper produced by electroplating.
 11. Processof claim 10 in which the copper coating is removed prior to thetermination of cold working.
 12. Process of claim 1 in which theenvelope consists essentially of a lead base glass and in which hermeticsealing to the protruding portion of the said reeds is accomplished byheating at least the encompassing portion of the envelope to atemperature of from 600*C to 1400*C and cooling to solidify theenvelope.